1. Field of the Invention
The present invention relates to medical instruments, and more particularly to an improved laryngoscope.
2. Background Information
The early need to visualize the larynx was for surgical purposes. As a medical student in 1829, Benjamin Guy Babington created a “glottiscope.” One shank held down the tongue while the other was positioned along the palate. Sunlight provided the illumination for a view of the glottis. The glottiscope was later termed the laryngoscope by his contemporary, Thomas Hodgkins. In 1844, surgeon John Avery developed a head-mounted mirror that reflected candlelight onto a mirror housed within a speculum. But it was Manual Garcia (1805-1906), a professor of singing at the Royal Academy of Music in London, who is generally credited with the discovery of laryngoscopy. In 1854, he utilized a dental mirror in combination with a hand-held mirror reflecting sunlight to visualize his own larynx and trachea during inspiration and vocalization. At the age of 100, he was honored by the most prominent laryngologists of his time as the Father of laryngology. A laryngology clinic was established in Vienna in 1870 and minor surgical procedures were performed under visual control. British surgeon William Macewen was the first to intubate the larynx for surgical purposes. He practiced blind, digital intubation on cadavers and eventually employed this technique to perform a composite resection in 1878. Pediatrician Joseph O'Dwyer worked at New York City's Foundling Asylum, where he developed instruments to enable tracheal intubation that saved the lives of hundreds of children suffocating from diphtheria.
Hans Kuhn modified O'Dwyer's instruments and created a long, flexible metal endotracheal tube and introducer, but his method still depended upon blind insertion, as light sources were inadequate to permit progress in direct laryngoscopy (DL). In 1895, Alfred Kirstein learned of an inadvertent tracheal insertion of an esophagoscope, and proceeded to develop a rigid laryngoscope with transmitted light. This consisted of a lamp within the handle, focused on a lens and redirected through the scope by a prism. Chevalier Jackson subsequently modified Kirstein's laryngoscope by providing distal illumination with a tungsten bulb. In 1913, Henry Janeway devised an open-sided laryngoscope with battery-operated distal illumination specifically for endotracheal intubation.
In 1941, Robert Miller introduced a new, longer, lower profile laryngoscope, which was designed to pick up the epiglottis. This blade required limited mouth opening but also left little space to manipulate the endotracheal tube (ETT). In 1943, Robert Macintosh described a curved blade to elevate the epiglottis by exerting its force on the base of the tongue. He believed that reducing contact with the epiglottis would be less stimulating and provide more room for manipulation of the ETT. Although both blades have been variously modified in the interim, they continue to dominate the field of laryngoscopy. Yet they both fail to provide an adequate glottic view in a small but significant number of patients.
Although there have been advancements in larygoscopy, e.g., fiber optics, varying techniques, lighted wands, and a number of technological modalities, the basic laryngoscope, which is far and away the most utilized instrument, has not materially improved since the early 1940s.
After years of clinical studies, it is clear that positioning alone does not align the mouth, pharyngeal and laryngeal axes and that force must be applied to achieve this. In any situation involving the care of a critically ill or injured person, the first consideration is always establishment and maintenance of the airway. It is estimated that failed intubation, especially in the emergency and austere environment, is the leading “preventable” cause of morbidity and mortality. In the pre-hospital environment, it is estimated that intubation success rates vary from approximately 85-95%. This compares to the approximate 99% success rates in hospitals. The main reasons for such a disparity are training, experience, resources, and technique.
The inability to see the larynx generally results in multiple or prolonged laryngoscopic attempts with increasing force, and is associated with esophageal, pharyngeal and dental injury, arterial desaturation, hemodynamic instability and unplanned intensive care unit admissions. An American Society of Anesthesiologists Task Force's definition of a difficult laryngoscopy states that “it is not possible to visualize any part of the vocal cords after multiple attempts” and a difficult tracheal intubation as one which “requires multiple attempts.” Though successfully accomplishing intubation is important, it is not enough. Intubation without an adequate laryngeal view should be regarded as a “near-miss,” which is incentive enough to improve airway management techniques and reduce reliance upon luck and multiple or forceful laryngoscopies.
The laryngoscope of the future will provide predictable laryngeal exposure and consistently successful intubation. It will be easy to learn, quickly performed and will impose less stress upon the patient. It will be inexpensive to acquire and robust enough to withstand the hostile environment of the pre-hospital setting as well as the operating room. It will not depend on sunlight for reliable laryngeal illumination.
Presently known prior art includes the following:
U.S. Pat. No. 4,570,614, which issued to Bauman on Feb. 18, 1986, teaches a laryngoscope with a single disposable nonmetallic blade, a light source disposed within the handle and a light conductor disposed adjacent to and held by the blade. Typical of the prior art, this apparatus requires two hands to operate, and perhaps even two caregivers, if the patient's mouth and head must be stabilized. Lacy (U.S. Pat. No. 5,355,870) and Bar-Or et al. (U.S. Pat. No. 5,702,351) also teach disposable plastic single blades used in combination with a light source in a laryngoscope.
U.S. Pat. No. 4,573,451, which issued to Bauman on Mar. 4, 1986, teaches a laryngoscope blade which has a tip that is capable being bent or flexed in the direction of the handle of the laryngoscope. This allows the patient's epiglottis to be lifted to expose the patient's larynx. This is a single blade instrument. It is provided with a ratchet lock to maintain the bend in the tip. This instrument can bend in only one direction, to lift the epiglottis. Locking the laryngoscope blade in an operable position is also shown in U.S. Pat. No. 5,651,760, but this lock/unlock mechanism functions to enable the instrument to be compact when it is not in use.
U.S. Pat. No. 5,036,835, which issued to Filii on Aug. 6, 1991, teaches a slideably adjustable spatula portion in the laryngoscope blade. The function of this spatula is to act as a tongue depressor to facilitate inspection of the pharynx and larynx, or the insertion of an anesthetic breathing tube. This apparatus uses a single blade with a sliding part, which does not lock in position.
U.S. Pat. No. 5,070,859, which issued to Waldvogel on Dec. 10, 1991, teaches a laryngoscope that incorporates a dynamometer in order to measure the force used by the caregiver to examine the patient. This invention is an attempt to avoid trauma to the patient that can occur using prior art apparatus.
U.S. Pat. No. 4,517,964, which issued to Upsher on May 21, 1985, teaches a dual bladed laryngoscope, wherein one conventional blade carries its own light source and the second blade is a light guide for a second light source in the handle of the instrument.
U.S. Pat. No. 5,498,231, which issued to Franicevic on Mar. 12, 1996. This apparatus is the current state of the art in the field of laryngoscopes. Franicevic teaches a reusable laryngoscope for use “in difficult intubation due to malformation of the jaws, tongue, pharynx, larynx or neck as a result of trauma, edema, inflammation or congenial anomalies.” This laryngoscope has a hollow body terminating at its distal end in a pair of opposed blades that can be spread apart by the caregiver. An endotracheal tube slides through the hollow tube in the center of the instrument. Light conducting means are provided to illuminate the larynx. The device includes a fiberoptic optical system for inspecting the larynx during intubation. Franicevic is an improvement on the “bendable tip” of Bauman, cited above. The single distal spreading of the “beak” taught by Franicevic allows some lifting of the soft tissue, but it does nothing to open the mouth or depress the tongue. Franicevic teaches a bias spring to keep the distal blades closed when they are not positively spread apart by the caregiver. This apparatus is not locking or self-retaining in the airway. It also is not disposable and its complex mechanism makes it difficult to adequately sterilize.
The closest prior art known to the present inventor is U.S. Pat. No. 5,938,591, which issued to Minson, the present invention, on Aug. 17, 1999. The '591 patent is a disposable self-retaining laryngoscopes used for orally intubating a patient with an endotracheal tube. However, this design ultimately failed in almost every configuration. The current invention is not similar to the '591 patent: the tongue blade, the palate blade and slider have all been changed significantly. Lengths, angles, and the configuration of the invention have all substantially changed relative to the '591 patent. For example, the fenestration of the improved palate blade allows removal of the laryngoscope over the endotracheal tube without displacing it. This is not possible with the '591 patent.
Despite all of the benefits from the limited improvements of the basic laryngoscope over the decades and the alternatives thereof, there still exists the need for an improvement in laryngoscopic technology at the most basic level to address the aforementioned issues. The number of different variations of laryngoscope found in the prior art is a good indication that many experts skilled in this art have tried to find solutions to these problems. Current technology requires that individuals “retract” the airway with one hand while attempting to intubate with the other. In fact, four hands may be needed to hold the head and mouth of the patient, operate the laryngoscope and intubate the patient. Therefore, an improved laryngoscope is needed that incorporates 1) hands-free application for simultaneous suction and intubation, which is especially important in trauma, and 2) improved and broader illumination. Until now, such an invention does not exist.